1. Field of the Invention
The present invention relates to vibrators that may be incorporated into mobile communications devices such as cellular phones and personal digital assistants (PDAs) to inform the user of an incoming call.
2. Description of the Related Art
Conventionally, mobile communications devices such as cellular phones and PDAs are arranged to inform the user of an incoming call by selectively generating beep sound or melody, or vibrating the housing of the device instead of producing sound. For this purpose, the conventional practice is to employ a structure incorporating a combination of a sound-generating speaker categorized as a microspeaker and a vibrator that generates vibration by rotating an eccentric weight with a small motor. Incorporating both the speaker and the vibrator as stated above, however, is disadvantageous from the viewpoint of achieving size and cost reduction of the device. Under these circumstances, use has recently been made of a magnetically-driven vibrator that can generate both sound and vibration by itself.
FIGS. 3 and 4 of the attached drawings show a structure of such a vibrator disclosed in Japanese Patent Application No. 2006-011087. As illustrated in the figures, the vibrator has a magnetic circuit assembly 21 including a substantially cup-shaped yoke 22 and a combination of a magnet 23 and a top plate 24 that are successively stacked in the yoke 22. An air gap (magnetic gap) g is formed between the inner peripheral surface of the side wall of the yoke 22 and the outer peripheral surface of the top plate 24. A voice coil 25 is inserted into the magnetic gap g. The voice coil 25 is secured to a substrate 26.
The magnetic circuit assembly 21 is supported by a first suspension 29 and a second suspension 27. The second suspension 27 has a tubular side wall portion 27a and a spiral leaf spring 27c integrally formed at a bottom 27b of the tubular side wall portion 27a. The spiral leaf spring 27c of the second suspension 27 is connected to the bottom of the yoke 22 of the magnetic circuit assembly 21 by laser welding or the like. A ring 28 is fitted to the inner peripheral surface of the upper end of the tubular side wall portion 27a to support the substrate 26 bonded thereto to close an upper end opening of the tubular side wall portion 27a. A ring-shaped weight 30 is secured to the outer peripheral surface of the yoke 22 as an additional weight. The second suspension 27 is covered in its entirety by a protector 31. The protector 31 has a bent portion 31a formed at the upper end thereof to retain the outer peripheral portion of the substrate 26. A shock absorbing member 32 is attached to the lower side of the substrate 26.
The first suspension 29 has, as shown in FIG. 4, an outer peripheral portion 29b, an inner peripheral portion 29c, and a pair of arcuate spring portions 29a provided in an annular space between the outer peripheral portion 29b and the inner peripheral portion 29c. The outer peripheral portion 29b is secured to the ring 28, and the inner peripheral portion 29c is secured to the top surface of the yoke 22 by laser welding. Specifically, the ring 28 is insert-molded together with the outer peripheral portion 29b of the first suspension 29.
In the vibrator having the above-described structure, the ring 28 used to secure the first suspension 29 to the tubular side wall portion 27a is insert-molded together with the outer peripheral portion 29b of the first suspension 29. Accordingly, the ring 28 requires a certain thickness and therefore may interfere with the vibration of the magnetic circuit assembly 21 when vibrating with a large amplitude. In addition, the arcuate spring portions 29a of the first suspension 29 are provided in a limited annular space between the inner peripheral portion 29c and the outer peripheral portion 29b. Therefore, the arcuate spring portions 29a cannot have a sufficiently long length and hence are likely to easily develop metal fatigue. It is necessary in order to minimize the metal fatigue to reduce the amplitude of vibration of the magnetic circuit assembly 21.